You can always patch the top till you can afford an upgrade. But definitely rust, especially if it comes from up north.
On another thread it was mentioned to get a little tiny hammer of some sort, I believe they said ball peen. tap on the frame lightly as you move around and listen. if you find a weak spot in the frame, for example rusting out from the inside so you wouldn't see it, you will hear the difference. Tap very lightly, if it is rusted bad enough and you punch through the owner will likely not be happy. The worst rust problems are the ones you can't see.